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July 2008

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From:
Ted Gaines <[log in to unmask]>
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Date:
Sat, 5 Jul 2008 03:30:04 +0000
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I agree Werner, the black pad venom. Can be fixed by Mid - P process. 



This is so accurate

Ted

Thank You,

Ted Gaines



-----Original Message-----

From:         Werner Engelmaier /* <[log in to unmask]>



Date:         Fri, 4 Jul 2008 22:33:12 

To: <[log in to unmask]>

Subject: Re: [TN] [LF] [TN] SN100 for Reflow Application





Hi Amol,

First, I would suggest you use a different lab in the future, or get them 

educated. The statements: " The presence of intermetallic at the interface shows 

that a “Black Pad” condition is not present." is pure nonsense.

Essentially, but not exclusivley, 'Black Pad' requires that IMCs are formed—th

at enriches the P-content at the Ni/IMC interface.

Second, the fact that you have 3 different failure modes—pad cratering, 

brittle interfacial separation, & BGA-side cracks, occuring, sometimes in 

combination, shows that you do not have a significant weak link. Some of the 

RoHS-capable PCB base materials are more brittle with lower cohesive strength, but 

seeing multiple failure modes indicates that is not the issue.

Third, you do not tell me what other processes follow reflow—however, 

whatever it is puts significantly higher stresses on the SAC-SJs than on the 

SnPb-SJs.

CONCLUSION: The root cause is obvious—it is the switch from SnPb to SAC and 

ALL that entails.

CRITICAL DIFFERENCES: A) SAC is about 40% stiffer than SnPb=>higher stresses;

B) delta-T to Tg of SAC Solidus v. SnPb Solidus is more than double=>higher 

stresses;

C) delta-T to Tg of SAC Soldering T's v. SnPb Soldering T's is more than 50% 

higher causing more warpage=>higher stresses;

D) SAC creep rates are about 50x slower than SnPb=>higher stresses.



I would suggest attending my new workshop Pb-Free Soldering Processes—

Survival, Quality, Reliability.



Werner

Future workshops:

Pb-Free Soldering Processes—Survival, Quality, Reliability, July 17/18, Thal, 

Switzerland

Pb-Free Soldering Processes—Survival, Quality, Reliability, August 18, 

Orlando

Reliability Issues with Lead-Free Soldering Processes, September 22, 

Schaumburg

Failure Mode and Root Cause Analyses Reliability (Fatigue, Brittle Fracture, 

ENIG), September 22, Schaumburg

Solder Joint Reliability: Parts 1 & 4, Oct. 9, Moscow, Russia

Solder Joint Reliability: Parts 1 & 4, Oct. 17, Timisoara, Rumania

Solder Joint Reliability: Parts 1 & 4, Oct. 22, Tallinn, Estonia







**************

Gas prices getting you down? Search AOL Autos for fuel-efficient used cars.

   

   (http://autos.aol.com/used?ncid=aolaut00050000000007)



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